Incandescent electric lamp



Patented Nov. 8, 1927.

UNITED STATES PATENT OFFICE.

JAN HENDRIK DE BOER, OF EINDHOVEN, NETHERLANDS, ASSIGNOR TO GENERALELECTRIC COMPANY, A CORPORATION OF NEW YORK.

INCANDESCENT ELECTRIC LAMP.

No Drawing. Application filed November 2, 1926, Serial No. 145,914, andin the Netherlands December 12,

This invention relates to electric incandescent lamps and moreparticularly to vacuum lamps provided with a tungsten filament. 1n theburning of the lamp the tungsten vaporizes and deposits upon the innerwalls of the lamp bulb, resulting in a harmful and undesirableabsorption of light.

Many ways have been suggested for diminishing such loss and absorptionof light. For instance, certain substances known as getters can bedisposed upon the internal.

walls of the lamp bulb or globe. The tungsten deposited by thevaporization of the filament upon the lamp bulb combines with thesesubstances and assumes a form in which less light is absorbed during theburning of the lamp than would be the case if the lamp bulb were notcovered by the getter. this purpose various fluorides have been used,for instance, calcium fluoride.

Applicant has found that the effectiveness of the getters heretoforesuggested and known is much enhanced by disposing a small quantity ofone or several salts of hydrofluorboric acid upon the inner walls of thelamp bulb.

According to the present invention, a salt of hydrofluorboric acid,either alone or mixed with other fluorides or other getters, forinstance, boric acid, is brought into the electric lamp bulb.Particularly good results are obtainable by the use of potassiumborofluorides.

The substances above referred to can be applied in any well known way,for example, by spraying or squirting an alcoholic solution orsuspension upon the filament before it is sealed into the bulb, thegetter being precipitated or deposited upon the lamp bulb byincandescing the filament after the bulb has been sealed.

To compare the getter action of calcium fluorides and potassiumborofluoride, it is convenient to use a curve which shows the decreasein the amount of current during the life of the incandescent lamp as afunction of the decrease in candle-power,

For

For a better understanding of what has ust been stated, it may bementioned that the decrease in amount of current is the consequence ofthe vaporization of the tungsten whereby the wire is attenuated. Thedecrease in candle-power or luminosity on the other hand is caused bothby the effect of decrease in current strength, and by the abing apotassium borofluoride getter; in other words, in the presence of equaldecrease in current strength and therefore of equal quantities ofvaporized tungsten, the corresponding decrease in candle-power isgreater when calcium fluoride is used than when potassium borofluorideis employed.

To further illustrate what has been pointed out above, the followingpractical figures may be cited. In the presence of a decrease of currentstrength of 3%, the reduction in candle-power is approximately 9.8% whencalcium fluoride is used, while with the use of potassium borofluorideit amounts to about 4.6%. After the decrease in current has reached 7%,the corresponding loss in candlepower amounts to 24.8% approximatelywith the use of calcium fluoride, and to 19.4% with the use of potassiumborofluoride.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An incandescent electric lamp comprisinga tungsten filament and asealed bulb having a salt of hydrofluorboric acid distributed in it tohinder absorption of the light by vaporized tungsten.

2. An incandescent electric lamp comprising a sealed bulb, a tungstenfilament in said bulb, and potassium borofluoride distributed on theinner Wall of said bulb to hinder abing a tungsten filament and a sealedbulb sorption of the light during operation of the containing a gettermaterial comprising a 10 lamp. salt of hydrofluorboric acid positionedin 3. An incandescent lamp comprising a said bulb to be activated andact as a getter sealed bulb, a tungsten filament in said bulb, when saidlamp is lighted.

and a getter on said filament comprising a In witness whereof, I havehereunto set salt of hydrofluorboric acid. my hand this 13th day ofOctober, 1926.

4. An incandescent electric lamp compris- JAN HENDRIK DEBOER.

